The present invention is generally directed to ink compositions useful in various imaging systems, and more specifically, the present invention is directed to certain ink jet printing compositions, and to processes for the preparation thereof. Accordingly, in one embodiment of the present invention, there is provided aqueous ink compositions comprised of modified polyimines, especially specific derivatives of polyethylenimines. The aforementioned ink compositions, in addition to possessing improved waterfastness, are of a desirable nonfishy odor; and further, these inks are free of environmental hazards in that they, for example, evidence a negative Ames factor, and thus are nonmutagenic. Also, the ink compositions of the present invention can be altered by adding thereto spreading substances such as benzyl alcohol, thereby enabling increased spot sizes. The ink compositions of the present invention also possess other desirable characteristics including a low pH, for example about 9, in a specific embodiment; low viscosity values; and further, the inks are stable at elevated temperatures.
Compositions which are useful in ink jet printing systems are well known, and generally contain water soluble dyes. There is thus disclosed, for example, in U.S. Pat. No. 3,846,141 an ink composition useful in jet printing comprised of an aqueous solution of a water-soluble dye; and a humectant material formed of a mixture of a lower alkoxy triglycol, and at least one other compound selected from the group consisting of a polyethylene glycol, a lower alkyl ether of diethylene glycol, and glycerol. According to the disclosure of this patent, the printing inks viscosity is subjected to little variation with use as water is lost by evaporation during recirculation of the ink composition through the jet printer. Moreover, apparently the humectant system disclosed in this patent substantially prevents or minimizes tip drying of the printing ink in the orifice or nozzle during down time of the printer, such as when the printer is rendered inoperative. As further disclosed in this patent, the basic imaging technique in jet printing involves the use of one or more ink jet assemblies connected to a pressurized source of ink. Each individual ink jet includes a very small orifice usually of a diameter of 0.0024 inches, which is energized by magneto restrictive piezo-electric means for the purpose of emitting a continuous stream of uniform droplets of ink at a rate of 33 to 75 kilohertz. This stream of droplets is desirably directed onto the surface of a moving web of, for example, paper; and is controlled to form printed characters in response to video signals derived from an electronic character generator and in response to an electrostatic deflection system.
Also, there is disclosed in U.S. Pat. No. 4,279,653 ink jet compositions containing water-soluble wetting agents, a water-soluble dye and an oxygen absorber. Similarly, U.S. Pat. No. 4,196,007 describes an ink jet printing composition containing an aqueous solution of a water-soluble dye and a humectant consisting of at least one water-soluble unsaturated compound. Further, there is disclosed in U.S. Pat. No. 4,267,088 coatings particularly useful as marking inks wherein there is selected an epichlorohydron-modified polyethylenimine, and an ethylene oxide modified polyethylenimine in an aqueous solution. Other patents that may be of interest are U.S. Pat. Nos. 4,101,329; 4,290,072; 4,383,859; 4,235,773; 4,279,814; 4,443,371; 4,286,989; 4,299,630; 4,167,393; 3,864,296; 4,238,234; 3,234,025; 4,520,143; 3,920,855; and 4,182,612.
Additionally, there is disclosed in U.S. Pat. No. 4,197,135 ink compositions with improved waterfastness comprised of at least one water soluble dye, and a polyamine with 7 or more nitrogen atoms per molecule. Specifically, there is illustrated in this patent an ink composition comprising an aqueous solution of at least one water-soluble dye, and about 0.5 percent to about 10 percent by weight concentration of a polyamine having 7 or more nitrogen atoms per molecule; and wherein the composition has a pH of 8 or above. In column 1, beginning at line 61, it is indicated that the preferred polyamines have the hydrogen of the primary amine group replaced with either a methyl or a hydroxyethyl group. Examples of fully substituted polyamines selected are outlined in column 2, beginning at line 40, of the '135 patent. The invention of the present application is directed to similar inks with the exception that the the amine, and more specifically, the polyethylene amine or polyethylenimine is not fully substituted thereby resulting in inks with improved waterfastness in comparison to those as illustrated in the '135 patent.
Ink compositions for jet printing can be prepared by a number of known methods. Generally, these methods involve dissolving the various dyes, humectants, viscosity control agents, paper fixing additives, surface tension control additives, biocides and anti-oxidants in a known volume of water, followed by adjusting the pH of the solution to desirable level. In those situations where the pigments selected are not water-soluble, the inks are prepared by standard known milling processes. However, such pigment dispersions are generally not sufficiently stable, accordingly when incorporated into a printing machine the ink particles tend to agglomerate resulting in the clogging of the small nozzles contained in the ink jet devices.
While the above compositions may be suitable for their intended purposes, there continues to be a need for improved ink jet compositions and processes thereof. Additionally, there continues to be a need for ink jet compositions which when in use result in superior optical print densities, and have excellent waterfastness characteristics. Moreover, there continues to be a need for inks that possess nonmutagenic characteristics enabling them to be safely used in ink jet printing processes. Also, there is a need for ink compositions that enable an increase in the spot size of the ink. Furthermore, there is a specific need for nonmutagenic ink compositions with a waterfastness of greater than about 80 percent.